How do "Instant Heat" patches work, chemically?

Factual Questions
1

I’ve used Instant Heat adhesive patches for menstrual pain, and, man, I just love em. It’s a tiny heating pad that lasts a good 12 hours, very comforting, and well worth the money.

So, I’m wondering how it works, chemically. Here are the ingredients, according to the package: Iron powder,water, activated carbon,vermiculite,salt, super absorbent polymer,natural mineral powder.

The patch is very flat to start with, and activated by exposure to air; no manual combining of different areas. By the end of the 12 hours, the patch is filled with granular rocky stuff. I cut one open to look, and it was reddish brown, the iron, I suppose.

These things are little miracle as to effectiveness. How do they work?

2

IIRC, the iron powder rusts very, very fast, thanks to added catalysts, generating heat.

3

YDRC.

(You do recall correctly :wink: )

4

::grumble:: ::grumble:: ::grumble::

I meant to add:

To elelle, “rusting” (or the oxidation of metals) can be a very powerful chemical reaction. If you take plain ole (but pure) iron oxide, and combine it with xxxxxxx (where “xxxxxxx” is some common metal, with its name withheld to protect the foolish from themselves), grind the two into a fine powder, you can create a thermitic reaction - one so hot you can use it to cut through metal, or fuse two metals together. Veeerrrry neat trick for the kids in chemistry class. (And a very hazardous potential bomb, if done incorrectly.)

-Geek

5

Haha, yes! Our science teacher in year 8 regaled us with tales of chem class in the bad old days, where teachers tossed chunks of sodium into pneumatic troughs of water (he says his old classroom still has a black mark on the ceiling), etched glass with hydrofluoric acid and, yes, made thermite and burned it. We begged him to let us make some. He said no. Something about regulations these days, pfffff.

6

Heh. My freshman (college) chemistry professor demo’d the thermite reaction for us. My favorite was the day he made chlorine gas, though. Just before the last step, he advised us that, although he had the fans on, it would be best if everyone exited the room as quickly as possible after the demo was complete. You know, just in case … :smiley:

7

Thanks for the answer, y’all. Im gonna call them “Rust pads” from now on.

They really do work well for cramps, and I suppose for back pain, etc. I see now that the package says, Made In Japan. A great little invention!

8

My high schol chem teacher pulled out the ol’ thermite all the time. He stuck sodium and potassium in water as well (though only tiny pieces.)

Hydrofluoric acid, though - I wouldn’t mess with that shit. That’s a bad, bad way to go.

9

Ah, memories. I saw the “sodium into water” stunt demo’d by my junior-high science teacher. He marched us outdoors first, though.

He also lit a piece of magnesium with a match, let us dabble our fingers in a beaker of mercury, and lit a cigar and blew the smoke through a paper towel to illustrate what is meant by “tar” levels in tobacco. He would be SO fired today, but I loved that class.